The present invention relates to a method of and apparatus for screening bulk material.
It is known to use pneumatic sifters for screening granulate bulk material. These pneumatic sifter are available in a wide variety of different designs, such as counterflow sifters, deflection sifters etc., and can be configured also as zigzag sifters. While in counterflow sifters, the sifting gas is conducted in opposition to the bulk material being screened, in deflection sifters the gas flow is typically conducted transversely to the flow direction of bulk material. Regardless of the type of pneumatic sifter being used, all designs require a very precise setting of the energy of gas, e.g. air, to be supplied. If the air energy is too weak, the separation of the fraction of fine particles will not be satisfactory. On the other hand, if the gas energy is excessive, the amount of coarse particles being entrained together with the fraction of fine particles is too high. This causes a problems, in particular, when different mixtures of bulk material are repeatedly screened, so that a correct adjustment of the air energy can normally be carried out only on the basis of empirical observation and only approximated.